Objective: To construct a cDNA expression library from unfed female tick Haemaphysalis longicornis for screening and cloning potential antigenic genes.
Methods: Total RNA was isolated from unfed female ticks, mRNA was purified and a library of oligo (dT) -primed cDNA with added directional EcoR I /Hind III linkers was constructed from the purified mRNA. The constructed cDNA was ligated to the EcoR I /Hind III arms of the lambda SCREEN vector. Pure phage stocks were harvested by plaque purification and converted to plasmid subclones by plating phage on host strain BM25.8. Recombinant plasmids that were subcloned to E. coli BM25.8 were isolated and transformed into E. coli JM109. Recombinant plasmids abstracted from JM109 were identified by PCR and sequencing.
Results: The recombinant phage DNA was packaged by using phage-marker packaging extracts, resulting in a primary cDNA library with a size of 1.8 x 10(6) pfu. Data showed 100% of the library were recombinant and the titer of the amplified library was 2.4 x 10(9) pfu/ml. Forty-two clones of encoding immunodominant antigens were obtained from the cDNA library. Sequence analysis revealed 12 unique cDNA sequences and the encoded putative proteins showed similarities to H. longicornis tropomyosin mRNA, Rhipicephalus annulatus unknown larval protein mRNA, chromosome 2R of Drosophila melanogaster, mitochondrial DNA of H. flava, clones HqL09 unkown mRNA and Hq05 mRNA of H. qinghaiensis, and myosin alkali light chain protein mRNA.
Conclusion: The cDNA expression library from unfed female H. longicornis was successfully constructed and screening of protective genes may provide candidate antigens of the tick.